Several normally wheeled vehicles and particularly light wheeled vehicles (e.g. ATVs, UTVs, SSVs, etc.) often have their wheels replaced by track systems which use an endless traction band instead of a tire for propulsion. Vehicles equipped with such track systems typically have improved floatation and better traction, particularly when they are operated over soft and/or rough terrains.
Over the years, most track systems used on light vehicles have come to have the same overall configuration. These track systems all have a drive wheel (e.g. a sprocket wheel) configured to be mounted to the wheel hub where the vehicle wheel was previously mounted, a support frame mounted either to the sprocket wheel or to the vehicle, front and rear idler wheels respectively mounted at the front and rear extremities of the support frame, road wheels mounted along the length of the support frame, and an endless traction band disposed about the sprocket wheel, the idler wheels and the road wheels.
This typical configuration of track systems generally defines a triangular-shaped envelop in which the drive wheel and the idler wheels define the three apices between which extends the traction band. Though this configuration of track systems has generally provided satisfactory results, it remains that it has at least two main shortcomings.
First, in such configuration, only the portion of the traction band that extends along the ground between the front and rear idler wheels (also referred to as the lower run of the traction band) actually contribute to propelling the vehicle. Indeed, only the lower run of the traction band is, at any moment, in contact with the ground surface. Though the remaining portion of the traction band (also referred to as the upper run of the traction band) is necessary for power transmission purpose, it only passively contributes to propelling the vehicle.
Understandably, this upper run of the traction band has a non-negligible mass that must be continuously driven to transmit power from the drive wheel to the lower run of the traction band. This, in turn, consumes valuable power.
Second, this configuration of track systems must generally be limited in size in order for the track system to fit on the vehicle while avoiding contacts with the frame and other components of the vehicle. In turn, this size limitation limits the size of the various components of the track systems, and more particularly limits the size of the drive wheel.
In that sense, it is to be understood that the size of the drive wheel ultimately affects the top speed of the vehicle. The smaller the drive wheel is with respect to the wheel it replaces, the lower the top speed of the vehicle will generally be. Though having a small drive wheel is not necessarily a problem when the vehicle is operated at low speed on rough terrains, having a small drive wheel can become problematic when the vehicle is operated at higher speeds on smoother terrains. In that sense, it is not uncommon nowadays to find vehicles equipped with track systems to be operated on relatively firm and even terrains such as trails or even paved roads.
There have been attempts to overcome or at least circumvent the traditional triangular configuration of track systems.
For instance, U.S. Pat. No. 6,874,586 discloses a track system in which the size of the drive wheel has been increased such as to contact the lower run of the traction band. Though such a track system has partially overcome the problem of top speed, it has done so at the expense of comfort since all the unevenness of the terrain will be directly transmitted to the drive wheel and thus to the vehicle and its operator. Also, the track system of U.S. Pat. No. 6,874,586 does not address the problem of the excess length of the upper run of the traction band.
For its part, U.S. Patent Application Publication No. 2006/0060395 discloses a track system in which the traction band does not wrap around the drive wheel. This track system thus uses a shorter traction band since it extends only between the idler wheels. However, the traction band is driven via its outer surface by multiple gears which are all mounted to the same frame, making the track systems less adaptable over uneven terrains.
Hence, there is a need for an improved track system which will mitigate at least some shortcomings of prior art track systems.